Treatment of Waste

Treatment of Waste

1. Treatment of Waste
OVERVIEW
The following brief discussion applies to all types of treatments, be it
for hazardous waste or refinery wastewater.
It should be remembered that:
1.Most Waste Generated is Wastewater
e.g. 214 million tons of hazardous waste generated in U.S. annually – of
which 97% is wastewater.
2.The constituents in wastewater must be either:
– Treated prior to discharge to a wastewater treatment plant
– Collected for disposal at a hazardous waste landfill
– Collected for treatment off-site.
3.Common Constituents of Industrial Wastewater
1. Suspended solids
2. Soluble organics
3. Toxic organics
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2. 4. Heavy metals and cyanide
5. Color and turbidity
6. Nitrogen and phosphorus
7. Refractory substances (resistant to biodegradation)
8. Oil and floating material
9. Volatile materials
4.Treatment of Industrial Wastewater: Depends on Final Destination
–Either sent to wastewater treatment plant – For additional treatment
–Or directed to the environment :
i.to surface water
ii.groundwater
iii.aquifer recharge
iv.direct use
5.Prior to discharge "wastewater" to any place:
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3. –Water must meet requirements developed by the local authority or your
industrial facility
–Discharge limits typically listed in a permit.
–Periodic sampling and analytical requirements are required.
Typical common limits set by authorities :
Biochemical oxygen demand
Chemical oxygen demand
Suspended solids
Fats, oils and grease
Heavy metals
4.Direct Discharge to Water Body
This requires a special permit and seldom given to any industry
In this case effluent must meet strict standards , and "point of discharge to the receiver
water" is usually set as well e.g. shallow vs.deep areas of water body.
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4. Types of Waste Treatment
Basically there are four types of treatment trains:
i.CHEMICAL TREATMENT
ii.PHYSICAL TREATMENT
iii.BIOLOGICAL TREATMENT
iv.THERMAL (INCINERATION)
The most important principle for effective treatments is to choose correctly the
required method of treatment. This correct choice depends on knowing:
i.Partitioning between water and air – Henry’s Law coefficient
ii.Partitioning between water and organics – Kow – octanol water
coefficient
iii.Biodegradability – Biodegradation rate constant
iv.Moisture content
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5. The following represents the basics of each type of treatments
I.Chemical Treatments
i.Catalysis
ii.Electrolysis
iii.Hydrolysis
iv.Neutralization
v.Photolysis
vi.Oxidation /Reduction
vii.Precipitation
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6. i.Catalysis
Basically, catalysis increase of rate and mechanism of a chemical reaction
e.g.
–complete air oxidation of cyanides
–dechlorination of chlorinated hydrocarbons
ii.Electrolysis
oxidation or reduction at an electrode surface immersed in a conductive
solution under the influence of an applied potential.
iii.Hydrolysis
Is a reaction of a salt with water to form an acid and a base
XY + Water ------> HY + XOH
iv.Neutralization
Means the adjustment of the pH by addition of either an acid or a base.
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7. This is carried out in continuous or batch reactors
v.Photolysis
Means the breakdown of chemical bonds under UV or visible light
vi.Oxidation / Reduction
Oxidation – Transfer of electrons from the chemical being oxidized to the oxidizing
agent (Cl2, O3, H2O2,KMnO4).
Reduction – transfer of electrons from the reducing agent to
the chemical being reduced, such as reduction of Cr
+6
(hexavalent state) to Cr
+3

(trivalent state) using sulfur dioxide
vii.Precipitation
Change in the solubility of compounds by addition of :
–alkaline agents (caustic soda or lime)
–sulfides (hydrogen and sodium sulfide are used to precipitate heavy metals)
–sulfates (cyanide removal)
–carbonates
Physical Treatment Processes
Trying to achieve one or more of the following:
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8. – Reduction of waste concentration
– Reduction of waste volume
– Separation of waste components
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9. Physical Treatment Processes include:
i.Adsorption
ii.Air Stripping
iii.Centrifugation
iv.Distillation
v.Electro - dialysis
vi.Evaporation
vii.Filtration
viii.Flocculation,
ix.Precipitation, and sedimentation
x.Flotation
xi.Freeze Crystallization
xii.Ion Exchange
xiii.Solidification
i.Adsorption :
a.Separates organics (and some inorganics) from an aqueous waste stream
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10. b. attraction and accumulation of the adsorbate (the organic) contained in water
or some aqueous phase onto the surface of a rigid, solid phase (the
adsorbent) such as activated carbon.
ii.Air Stripping
a.Volatile components are transferred from a liquid mixture (water) to a gas
(air).
b.Driving force is related to the departure of the vapor-liquid phase
concentrations from equilibrium with mass transfer in the direction of
decreasing concentration.
iii.Centrifugation
a.Centrifugal force is used to separate liquid from the solid in enclosed
environs.
b.Primarily used to dewater sludge resulting in a reduction of the sludge
volume.
c.Reduce slurry volumes
d.Results in an increased solids concentration in the waste streams.
iv.Distillation
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11. a.Nondestructive liquid phase separation process
b.Used for organic component recovery
c.Based on differences in vapor pressure
v.Electrodialysis
a.Separates ionic components of a waste stream
b.Uses synthetic membranes and an electrical field
–membrane is a semi-permeable one, allowing either anions or cations
to pass through it
–electric field causes separation of positive from negative ions
iv.Evaporation
a.Concentrates the waste and reduces its volume by heating the mixture in
pipes, ponds
b.The vapor phase is not collected and/or condensed as in distillation.
v.Filtration
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12. a.Liquid passes through a porous media that traps the solids
Typical media: Sand, Porosiline
b.Backwash to clean filter,
vi.Flocculation, Precipitation, and Sedimentation
a.Removes suspended solids, colloids
b.Enhance conditions for floc formation
i. Changing solubility of metals
ii. Settling chamber
c.Flocculating particles aggregate or coalesce thereby changing the
particle size, shape, and even specific gravity.
vii. Flotation (Dissolved Air Flotation DAF)
a. removes solids suspended in the waste
– via agitation
– sometimes via chemical addition
b. Air bubbles reduce the solid density
– Bubbles carry particles to the surface of the tank.
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13. c. A froth or foam forms at the top and contains
the solids
–removed with a skimmer arm
viii.Freeze Crystallization
a.The waste water is cooled to form purified ice
b.crystals
c.Remaining liquid will be more concentrated
d.The process can be repeated on the same waste to further concentrate
ix.Ion Exchange
a.A synthetic or natural resin material
b.Used to removed dissolved solids
c.Heavy metals and anions attach to the resin surface, exchanged for other
anions that were previously on the surface
d.Occurs quickly, unless/until all the exchange sites are filled
– “Breakthrough” – requires regeneration.
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14. x.Solidification
a.Fixes or encapsulates the waste
Rendering the Hazardous Waste into a non-hazardous solid product
b.Solidifying agents:
–Silicates
–Cement-based (Portland is common; results in rock-like solid)
–Lime-based
–Thermoplastics
–Organic polymers
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15. Biological Treatment
As the name implies, it uses microbes to decompose organic wastes. During the
process of biodegradation, sorption and stripping also occur.
Types of Biological Treatment
1.Aerated lagoons
2.Activated Sludge
3.Anaerobic Digestion
4.Composting
5.Enzyme Treatment
6.Trickling Filters
7.Waste Stabilization Ponds
i.Aerated lagoons
Three types of lagoons 3-5 meters deep are used:
– Well mixed (all aerobic)
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16. – Facultative
– Settling lagoons
The treatment efficiency depends on many factors:
– Oxygen availability
– Waste biodegradability
– Nutrients (N & P)
– Detention time
ii.Activated Sludge
Similar to aerated lagoons in operation. Usually 2 stage process viz:
– Aeration basin
– Clarifier
Some microbes are wasted, others are returned to the system (“activated”)
iii.Anaerobic Digestion
Uses microbes that do not need oxygen to respire
Not usually suitable for industrial wastes
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17. iv.Composting
Land reclamation, land-farming.
Biodegradation of organics in the soil.
Requires collection of leachate and runoff for groundwater protection.
Can aeration by turning the soil.
v.Enzyme Treatment
An enzyme must be added for the process to start.
Speed up degradation of the waste.
Applicability limited to simple waste streams:
– Enzyme is specific to target wastes
– Inhibited by some inorganics
– pH sensitivity
vi.Trickling Filters
Microbes are supported on a solid media structure (e.g., rock, plastic)
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18. Wastewater is trickled over the media
There is a biofilm layer consisting of:
– Aerobic outer layer
– Inner layer may be anaerobic
– Waste concentration changes within the biofilm
vii.Waste Stabilization Ponds
Basically, the method dilutes industrial wastes and uses shallow basins (1 to
2 meters) deep
Wind provides limited aeration but at the bottom of deep ponds the processes
mainly are anaerobic at the bottom.
Photosynthetic algae of surface
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19. Post-Treatment: Equilization
The object from post-treatment can be summarized in the following six
points:
1. Prevents shock loading of biological systems by dampening
organic fluctuations.
2. Enables better pH control, and can reduce chemical requirements
for neutralization.
3. Minimizes flow surges to physical/chemical treatment systems.
4. Provides continuous feed to biological systems
5. Enables controlled discharge of treated wastewater to end points
thus enabling even distribution of the wastewater load.
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20. 6. Prevents high concentrations of toxics from entering the biological
treatment plant too rapidly.
I.Primary Treatment
This basically a physical treatment – settling basins
It uses gravity to remove suspended solids
It also employs screens, grinders, grit removal…etc.
II.Secondary Treatment
Standard type of a secondary treatment consists of:
Biological Treatment
– Aerobic type such as:
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21. Aerated lagoons
Activated sludge
Trickling filters
– Anaerobic type such as:
digesters
III.Tertiary/ Advanced Treatment
This takes secondary treatment further by filtration to remove solids from
treated wastewater and removes nitrogen and phosphorous compounds. By this
treatment treated wastewater can be converted to potable water. The use of
ionexchage systems are widely used.
IV.Ultimate Disposal Options
Following treatment, remaining wastes often disposed to land such as:
–Waste streams remaining from the wastewater treatment at the
industrial site
–Solid wastes not discharged to sewer
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22. –Solids/sludge from the wastewater treatment plant
V.Land farming
There are many options to get rid of solid organic waste. One such method
is land farming. In this method ploughing land is carried out first, and then only
organic degradable waste is sprinkled evenly. Ploughing is repeated till upper
layers of soil are homogenized. This is a cheap, effective and simple disposal
method. Above all, the method enhances soil. One should remember that
degradation factors depend on:
– Waste Composition
– Contact between the waste and the microbes
– Soil Temperature
– Soil pH
– Oxygen
– Inorganic Nutrients- N & P
– Moisture Content
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23. If the treated "waste" is liquid, then another method can be used, namely:
Deep Well Injection. The method depends on transferring of liquid waste deep
underground far away from freshwater sources.
Criteria for "waste" waters in this method are:
– Low Volume, High Concentration Waste
– Difficult to treat by other methods
– Compatible with material in disposal zone
– Biologically Inactive
– Non corrosive
VI.Incineration
Destruction of wastes by Combustion
The method is suitable for:
– Gases
– Liquids
– Slurries
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24. – Sludge wastes
– Solids
– Containerized
Incineration destroys molecular structure, thus molecules with more stable structures
and stronger chemical bonds require longer residence times and/or higher
temperatures.
Incinerator operating conditions must be monitored continuously. The following are
some parameters affecting the efficiency of burning:
Combustion temperature
Residence time
Degree of mixing
Presence of excess air
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25. The type of incinerator required depends on the chemic and physical state of "waste"
.Examples of incinerators:
Liquid injection
– Any pumpable waste
– Converts liquid waste to gas prior to combustion
Kilns
– Used on solids, liquids, and gases
– Many different types (e.g., rotary kilns, cement kilns, lime kilns,
aggregate kilns).
Calcination or sintering
– 1800oC and atmospheric pressure.
– Destroys organics; reduces the volume of inorganics
Incinerator Performance must be monitored, thus:
Destruction and Removal Efficiency (DRE) must be determined. This done by
"monitoring" organization. The higher the figure of DRE , the more efficient is the
incinerator.DRE of 99.99% for all “principal organic hazardous constituents”
(POHCs) is required.
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26. – Example: Wastes containing dioxins and furans
requires 99.9999% DRE
Incomplete combustion – afterburners must be installed for exhaust
– Combust the exhaust at higher temperature than the combustion of
primary waste stream. Example: dioxin and furan creation, more toxic than
precursors
75 dioxin congeners; 135 furan congeners
Incinerators usually produce particulates; thus particulate controls are important.
Particulates can be removed by using bag-houses, and water scrubbers
Control of acid formation is also important e.g. HCl from combustion of
chlorinated organics. Acids corrode metals and form "acid precipitates", and acid
rain.
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27. Landfill
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28. 28

29. Recycling is important for several reasons.
1) Recycling conserves natural resources. i.e., they don’t get replaced as we pull them out of the ground. Once they’re gone,
they’re gone forever.
2) Recycling conserves landfill space. Landfill space will last longer if we only put items that are not recyclable into them. It
costs a great deal of money to build a landfill and we need to be careful how much and how fast we fill them up.
3) Recycling employs people. Recycling employs people who
i.Collect the recyclable material,
ii.Process the material or get it ready to sell to a manufacturer,
iii.Transport the materials to factories where it will be turned into new products,
iv.Take the material and manufacture it into new products,
v.Manufacture equipment and products used by the recycling industry, and finally
vi.Manage recycling programs and private and non-profit recycling programs.
4) Recycling conserves energy. Without question, recycling conserves the energy that would be necessary to create the same
product from its raw resource.
5) Recycling reduces our dependence on overseas natural resources. This is important in two very important ways:
i.It reduces our dependence on overseas oil and gas which has national security implications
ii.It reduces our foreign trade deficit which is important to the strength of our economy.
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30. (H enry's law can be put into mathematical terms (at constant temperature) as
where p is the partial pressure of the solute in the gas above the solution, c is the concentration
of the solute and kH is a constant with the dimensions of pressure divided by concentration.
[1]
The
constant, known as the Henry's law constant, depends on the solute, the solvent and the
temperature.
Some values for kH for gases dissolved in water at 298 K include:
oxygen (O2) : 769.2 L·atm/mol
carbon dioxide (CO2) : 29.41 L·atm/mol
hydrogen (H2) : 1282.1 L·atm/mol
Octanol-Water Partition Coefficient (KOW) - "An organic compound's octanol-water partition
coefficient, KOW, is defined as the ratio of the compound's concentration in a known volume of
n-octanol to its concentration in a known volume of water after the octanol and water have
reached equilibrium ... Water solubility was found to be the major factor affecting the partition
coefficient." – Smit
Biodegradability:
What exactly does this mean? I would define it as being able to be broken down by natural
processes, into more basic components. Products are usually broken down by bacteria, fungi or
other simple organisms. By this definition, most chemicals are biodegradable; the only thing
differing would be the amount of time it takes to break down. A piece of bread will break down
rather quickly, whereas a piece of plastic will take decades and beyond.
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31. Volume reduction
Volume reduction includes those techniques that remove the hazardous
portion of a waste from a non-hazardous portion. These techniques are
usually to reduce the volume, and thus the cost of disposing of a waste
material. The techniques that can be used to reduce waste-stream volume can
be divided into 2 general categories:
1.source segregation and
2.waste concentration.
Segregation of wastes is in many cases a simple and economical
technique for waste reduction. Wastes containing different types of
metals can be treated separately so that the metal value in the sludge can
be recovered. Concentration of a waste stream may increase the
likelihood that the material can be recycled or reused.
Methods include :
-gravity and
-vacuum filtration,
-ultra filtration,
-reverse osmosis,
- freeze vaporization etc.
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32. What Is Biological Oxygen Demand And How Does It Affect Water Quality?
Biochemical oxygen demand is a measure of the quantity of oxygen used by
microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter. Natural
sources of organic matter include plant decay and leaf fall.
Chemical oxygen demand (COD) is used as a measure of oxygen requirement of a
sample that is susceptible to oxidation by strong chemical oxidant. The dichromate
reflux method is preferred over procedures using other oxidants (eg potassium
permanganate) because of its superior oxidizing ability, applicability to a wide variety
of samples and ease of manipulation. Oxidation of most organic compounds is 95-
100% of the theoretical value.
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33. Source of e-wastesConstituentHealth effects
Solder in printed
circuit boards, glass
panels and gaskets in
computer monitors
Lead (PB)
·Damage to central and peripheral nervous systems,
blood systems and kidney damage.
·Affects brain development of children.
Chip resistors and
semiconductors
Cadmium
(CD)
·Toxic irreversible effects on human health.
·Accumulates in kidney and liver.
·Causes neural damage.
·Teratogenic.
Relays and switches,
printed circuit boards
Mercury
(Hg)
·Chronic damage to the brain.
·Respiratory and skin disorders due to bioaccumulation
in fishes.
Corrosion protection
of untreated and
galvanized steel
plates, decorator or
hardner for steel
housings
Hexavalent
chromium
(Cr) VI
·Asthmatic bronchitis.
·DNA damage.
Cabling and
computer housing
Plastics
including
PVC
Burning produces dioxin. It causes
·Reproductive and developmental problems;
·Immune system damage;
·Interfere with regulatory hormones
Plastic housing of
electronic
Brominated
flame
·Disrupts endocrine system functions
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34. equipments and
circuit boards.
retardants
(BFR)
Front panel of CRTsBarium (Ba)
Short term exposure causes:
·Muscle weakness;
·Damage to heart, liver and spleen.
Motherboard
Beryllium
(Be)
·Carcinogenic (lung cancer)
·Inhalation of fumes and dust. Causes chronic
beryllium disease or beryllicosis.
·Skin diseases such as warts.
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